Producing flat-set copper shapes



Sept. 23, 1941. P. M. HULME ETAL PRODUCING FLAT-SET COPPER SHAPES Filed001'.. 3C`), 1940.`

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Ro 63mg Sept. 23, 1941. P. M. HULME ET AL.

PRODUCING FLAT-SET COPPER SHAPES Filed Oct. 50, 1940 2 Sheets-Sheet 2INVENTORS PHILIP M. HULME ROBERT A.

GHELARDI ATTO R N EY5 Patented Sept. 23, 1941 Pnonucmo FLAT-sor corro-n.sucres Philip M. Holme and Robert A. Ghelardi, Meituchen, N. J.,assignors to International Smelting & Refining Company, a corporation ofMontana Application (ictoher 30, 1940, Serial No. 363,5?18

`(Cl'. 'i5-76) 9' Claims.

This invention relates to the production of substantially flat-set castcopper shapes, and has for its object the provision of an improvedmeth-v od for producing such shapes. Y

Most of the copperbeing produced commercially at the present time iselectrolytically refined. Such copper is very pure, lbut physically itis unsuited for rolling, drawing, or other fabricating operations forproducing commercial articles. Accordingly, it is necessary to melt thecathode copper produced by electrolytic refining methods and cast itinto wire bars, billets, cakes, or other shapes from which commercialarticles may be made.

The common practice for melting and casting electrolytic cathode copperheretofore has followed the old Welsh process for fire-reining, and isin fact known as a reningf process. It involves first melting the copperin a fuel-fired furnace, skimming any slag formed, oxidizing the moltencharge, skimming the oxidized impurities, and then poling the charge toreduce cuprous oxide. During the melting operation the copper is incontact with the gaseous combustion products of the fuel, and some ofthese gases are absorbed in and contamina-tothe copper. To remove thesecontaminants and other impurities, the molten copper is blown with airand then skimmed. In this manner impurities in the copper are largelyremoved, but some copper oxide is unavoidably formed and remains in themolten copper. The molten copper, therefore, is next covered with cokeand subjected to a poling operation by plunging wooden poles below thesurfacev of the molten metal. As a result of this operation, the cuprousoxide in the molten metal isV reduced and the metal is conditioned forcast- The progress of the pcling operation is carefully watched bytaking frequent samples and casting them into blocks. Whether or not thepoling operation has proceeded to a sufcient extent is determined byobserving the nature of the set or pitch, that is, the condition of theexposed surface of these cast samples upon cooling. When the testsamples show a proper set, poling is stopped and the molten copper iscast into suitable shapes.

The cast product solidifying in the mold with a substantially flat orslightly crowned surface, or set, is known as tough-pitch or flat-setcopper. This copper invariably contains a small amount of oxygen (0.01to 0.05%), as-the presence, of av small amount of oxygen is necessary toinsure the flat-set desired for rolling and Cilv drawing operations.IThe precisel mannerL in which the oxygen functionsto producefa' flat-setis not fullyv understood, but it is generally bee lieved that the'oxygen reacts with very' small amounts of impurities (partioularlysulphur) present even in cathode copper,` andl formsa gas which comesout of solution as-V the copper cools. |This gas expandsy andcounteracts.f the tendency of metallic copper to shrink upon'freezingb-y forming minute-cavities in the castingin sufcient amount topreventt'he formation of` a shrinkage cavity or pipe Ifinsufficientgasis evolved, the surface willbe depressed; or' ifthereistoo muc-h, the surfacewllfraise andrnay even be broken by a spew ofmetal forced throughthe frozen surface scum. The former is known aslow-set copper'and the latter as crown-set copper, or over-poled copperwheremetal has been forced or spewed through the frozen5scum. Only theflat-set or slightly-crowned copper is properly called-tough-pitchcopper, since by'long usage the term tough-pitch has come to` des-`ignate copper which uponl casting solidifiesy with this desirablel set.-Althoughy true4 toughepitch copper invariablyy containsabout 0.01 %Y to-0.05% oxygen, the term tough-pitch may' not properly be applied to anycopper containingthis amount of oxygen, for in some cases` (dependingupon the amounts-of impuritiessuch as sulphur, in the copper) thepresence otoxygen within these limits will not produce the fiat-set orslightly crowned setrequired for commercial purposes. Y

Because ofthe commercial importance of'producing true toughfpitch coppercastings,vv the pol'a ing operation of the refining-,process must bevery closely watched., andthe melting andcasting of copper by thisprocess is truly an art requiring longy experience to master, vratherthan a process subject to scientific control. Attempts have heretoforebeen made to simplify the process, but exceptfor improvements ofamechanical nature for lightening the hand work involved, these attemptshave been unsuccessfulandthe metallurgy of the process has remainedhkunchanged. 1 In addition to being difcult to` controlm properly, therefining process is subject to other disadvantages which heretofore havenot been overcome. One of these disadvantages is thatv the process isinherently a batch operation. ach furnace charge must be heatedlandmelted,.oxi dized and poled before casting canA commence, and so thecasting operation, during whi'chtime the furnace is actually producing an'iarllzetable product, is limited to a small fraction of the timerequired for each cycle f operation. In the case of the usualtwenty-four hour cycle, for example, casting proceeds for only about vehours. Attempts heretofore made to make the melting and castingoperation continuous have been unsuccessful.

A further disadvantage of the refining process is that it imposes severetreatment on the furnace employed. The alternate heating and cooling ofthe furnace refractories due to the repeated emptying of molten metal,charging with cold metal, and again melting, results in extensive heatlosses and causes the furnace refractories to crack and spall. Theaverage life of a furnace used in the refining process is only about veto six months.

In recent years, certain processes for the production of oxygen-freecopper of high electrical conductivity have been developed. Suchoxygenfree copper possesses certain desirable properties for a number ofuses, and in view of the success that has been attained in itsproduction, it might appear that the production of tough-pitch copper isldoomed to obsolescence. Actually, however, this is not the case, fortough-pitch copper possesses some advantages over even oxygen-freecopper. Moreover, the production of oxygen-free copper by the processesnow available is expensive, and the demand for the consequentlyrelatively expensive oxygen-free product is limited.

By far the greater amount of copper now being sold is the less expensivetough-pitch copper, and it is likely that it will continue to be themost common form of copper sold for many years to come. f

The present invention provides an improved method for producingtough-pitch or flat-set cast copper shapes in a manner that overcomesthe disadvantages of the heretofore customary refining process. Inaccordance with the invention, substantially oxygen-free copper (e. g.cathode copper) to be melted is introduced into the melting chamber of afuel-fired mule furnace and therein is heated and melted largely byradiant heat. In this manner the copper during melting is kept out ofcontact with combustion gases, and so is not contaminated thereby duringmelting. A gaseous non-oxidizing (and preferably reducductivity. A bathof substantially oxygen-free molten copper is established and maintainedin the melting chamber under conditions permitting unhindered transferof radiant heat to the surface thereof. In other words, no medium ofrelatively poor heat conductivity,` such as slag, charcoal and the likecovers the surface of the molten metal. The copper to be melted isintroduced into the melting chamber under conditions substantiallyinhibiting the introduction of air into the chamber, and fuel isintroduced and burned `in the combustion chamber above the arch in aing) atmosphere is maintained in the melting manner to heat the arch andestablish and maintain at its under surface a temperature at least equalto the melting point of copper, and preferably several hundred degreesthereabove. The copper in the melting chamber is melted largely by heatradiated thereto from the arch, while maintaining the aforesaidslag-free bath of substantially oxygen-free molten copper.

It has been found that the surface of the copper in the melting chambershould be maintained substantially free of reactive fused slag. Thepresence of such slag interferes with the transfer of radiant heat tothe metal charge, and may attack the refractory lining of the meltingchamber unless expensive refractories resistant to such attack areemployed. It may be advantageous, however, to maintain on the surface ofthe copper in the melting chamber a layer of finely divided refractorymaterial having a relatively high emissivity and of good heatconductivity, such as finely divided or granular silicon carbide. Such alayer may improve the transfer of radiant heat to the furnace charge.

The copper to be melted advantageously is charged continuously into thefurnace and molten copper is withdrawn continuously therefrom forcasting. The copper may be withdrawn through an open launder, with alayer of charcoal being maintained over, but not completely covering,the surface of the copper flowing through the launder. The amount ofcharcoal so employed is controlled so as to control the area of copperexposed to the air in a manner to permit incorporation in the copper ofa proper amount of oxygen to produce a fiat-set upon casting andcooling.

The oxygen-bearing product flowing from the launder is cast in anydesired manner into suitable shapes.

The invention will be better understood from the following description,considered in connection with the accompanying drawings, in which Fig. 1is a longitudinal cross section through a furnace suitable for use incarrying out the invention; and

Fig. 2 is a horizontal cross section taken substantially along the line2 2, of Fig. 1.

The furnace shown in the drawings comprises side walls I0 and II anden-d walls I 2 and I3 of refractory brickwork. The furnace is providedwith a refractory iioor I4 adapted to support a body of molten copper,and an arched masonry roof I5 of refractory brick. The furnace is bracedby vertical buckstays I6 and I'I connected by horizontal tie-rods I8 andI9 above and below the furnace. To conserve heat and enable developmentof adequately high temperatures (which the brickwork must besufficiently refractory to withstand), the roof of the furnace iscovered with a layer of insulation material 20 and the walls areinsulated by layers of insulating brick 2l and 22.

The interior of the furnace is divided into a mufle or melting chamber23 and a combustion chamber 24 by means of a melting chamber arch 25sprung between the side walls of the furnace. The arch 25 is relativelythin and of highly refractory material possessing good heat-conductingproperties. The most satisfactory refractory material for the arch issilicon carbide (e. g, that known commercially as Carborundum), which ismechanically strong, highly refractory, and

g possessed of fairly good properties as a heat conductor. The archshould be as thin as it is practical to make it in order that there willbe a gesamt maximum heat transfer therethrough. Silicon' carbide issufficiently strong mechanically toenable construction of a thin arch,of the order of a few inches in thickness, about six feet or sov wide.

The arch is sprung between refractory blocks 25 extending the length ofthe furnace; Advantageously these refractory blocksv also are of siliconcarbide. K

Gil burners 2l extend into the interior of the combustion chamberZ'through one end'wall i2 of the furnace. A iiue 2S' at thel oppositeend of the furnace is provided for the Withdrawalof combustion gasesIfrom the combustion chamber.

One or more charge openings 2i) are provided in the side Walls of thefurnace for introducing copper to bem-eltedinto the meltingfchamber-2-3;The charge opening 29 slopes downwardly toward the melting chamber.Copper cathodes are passed to the charge opening througha` charging lockiclosed by two doors Sil hinged attheir upper ends. The oor of thecharging lock 3S slopesin conformity with the charge opening so that'cathodes may be slid easily into the melting chamber. hibits theintroduction of air into the melting chamber and thus aids inmaintaining the con templated non-oxidizing atmosphere in the meltingchamber. A vent stack 32 may be provided at the outer end of the`charging lock for the Withdrawal of gases leaking from the furnacethrough the lock.

Gas inlet conduits 33 extending through thev side walls of the furnaceare provided for introducing gas into the melting chamber 23 for thepurpose of maintaining therein an atmosphere of the desired composition.

A tap hole 3'!! is provided in the end wall l2 of the furnace forwithdrawing molten copper therefrom. The tap hole may be partially orwholly plugged with clay, and the clay may be gradually broken down forintermittent tapping, or the tap hole may be left open for thecontinuous run-out of metal in continuous operations. The tap hole opensinto a launder 35 for conducting molten copper to a tilting pouringladle or furnace or other suitable casting equipment not shown).

A curtain wall 3S may be provided in the furnace adjacent the tap hole313. A single opening El through the curtain wall is disposed adjacentthe bottom thereof below the normal level of molten copper in thefurnace. A normal depth of molten copper in the furnace forms a liquidseal of the opening through the curtain wall, without preventing out-nowof the copper. In combination with the curtain wall, this liquidsealeectively excludes air entering through the tap hole from passinginto the melting chamber behind the curtain wall. per in the furnacebetween the tap hole and the curtain wall may be covered with charcoal,if necessary, to protect it from the air.

In practicing the invention, copper to be melted is introduced throughthe charging lock 3S and the charge opening 29 into the melting chamberunderneath the inciting chamber arch 25. Fuel oil is admitted throughthe burner 21 and burned inthe combustion chamber 24 above the arch 25in a manner to heat the arch and establish and maintain at its undersurface a temperature at least equal to the melting point of copper. Themelting chamber is heated largely by radiant heat from the arch 25, andto a lesser extent by heat conducted through the side and end walls:

Qf-'thefurnace' Pure copper melts at a temper- The charging lock 3Bsubstantially in- The small body of copetere of: about' 19eo andaccordingly therein;

perature `maintained"at the under-surfacefof the archl must at leastlequal-thisv value in'y order' to meltcop'per largely by radiationfofheat to it from the'. arch. For practic-alfpurposes, however, itisdesirable to heat the molten? copper to' a temperatureV of' about 2050Ff in'l order to secure satisfactory casting results, andJ inorder toachieve an adequate melting ratezinlthe furnace for economic.commercialop'erations; itis desirable to maintain! ar` t'enfipenfature-vconsiderably higher even than' this figure 'at the under surface of thearch.. Accordingly'atemperature of-about 25G0 F. preferably ismaintainedat. the under surface of the arch.4

Since the-copper int` the melting chamber 23ris melted largely byheatra'diated to itfrom thev un der surface-'of the archyit isimportant` to establish and vmaintain?conditions favoring `thetranslferoffradiantheat' to the-copper.- Oneisuch conidition is theemissivity ofv the material at ,the surfaceofthecharge. In asense'thisemissivity is a measurei of=thefability ofl the charge toabsorb the heatv radiated: to it. The emissivity: of molten copperisadequately highto lenable meltingto proceed at a reasonable ratewhenthetemperature `at the under surface of the arch ismaintai-ned-sufciently high (at'about 2506" FJ.

Fused slags generally possesshigher emissivitiesithan molten coppen-butthey are poor conn ductors of heat. If` present onthe surface ofl themolten copper, they impede rather than. aid in the-transfer of heatto-vthezcopper. Since reactive fused slags yare not required inthemelting chamber to remove iimpuritiesfrom the'copper, theirpresenceisundesirable,.and in the preferred practicebfthe invention careVisiexercised Vto maintain the surface of the` moltenv coppersubstantially free of such slags.`

Reactive fused slags also have been found' objectionable for the reasonthatfthey4 are apt to attack the refractory lining of theside walls ofthe melting chamber. MoltenA copperA which-is substantially. free ofoxygen or oxides4 exerts practically no effect upon commonandinexpensivesilica refractories, so that suchrefractories may be employedl inconstructing the melting chamber side Walls. Many. fused reactiveslags,however, quickly attack silica refractori'easo that the presence of slagin the meltingchamber, while accomplishing no usefulV purpose,necessitates the use of'expensve refractorie's resistant to such attack,or results in serious damagev to the furnace linings.

It has heretofore been proposed to deoxidize molten copper bymaintainingv a layer ofl charcoal on the surface thereof'. Such Va layerof charcoal would perform no' useful purpose in the practice of the`present invention, and would moreover be objectionable since itsrelatively poor heat conductivity would impede the transfer of radiantheat to' the molten copper. .The presence of charcoal on the surfaceofthe molten copper is apt to be attended by the further dis- 'advantagevof coating the under-side of the arch 25'with a nlm of finely dividedcharcoal which may objectionably decrease the heat. conductivity'of thearch.

While the surface of the molten copper in the melting chamber is-'freeof slag and of anyy other medium impeding the transfer of radiant heatthereto, floating' patches of'unfused orr partially fused refractorymaterial may gather on the surface of the molten copper. Where themelting chamber is lined` with. silica brick, -theseffloatingpatchescon's'st mainlyv of'silica and appear to be due to mechanicalerosion of the lining by the molten copper.y This has been observed tooccur to a small extent in a newly-lined furnace when it is rst put inoperation. So long as these floating patches cover in the aggregate onlya small part of the surface of the molten copper, they are of nopractical significance. However, they should be raked or pulled off thesurface of the molten copper from time to time, in order to insureefficient transfer of radiant heat to the surface of the molten copperas well as effective direct exposure of the surface of the molten copperto the gaseous reducing atmosphere.

The copper in the melting chamber is kept out of contact with thecombustion gases of the fuel by means of the melting chamber arch 25,and so is not contaminated from this source. A bath of substantiallyoxygen-free molten copper is established and maintained in the meltingchamber, and a non-oxidizing, and preferably reducing, atmosphere ismaintained above the surface of the molten copper. A satisfactoryreducing atmosphere is one of charcoal producer gas consistingpredominantly of carbon monoxide and nitrogen, say about 25% carbonmonoxide and about 75% nitrogen. Under favorable operating conditions,nitrogen alone may be employed, but it is relatively expensive, and thereducing quality of carbon monoxide is usually advantageous, and may benecessary, to establish and maintain the desired bath of substantiallyoxygen-free molten copper.

The non-oxidizing (or reducing) atmosphere above the molten coppershould be free of any constituent capable under the operating conditionsprevailing within the `melting chamber of deleteriously affecting theoxygen-free molten copper. The presence of hydrogen should be avoided,since hydrogen is readily absorbed by molten copper, and adverselyaffects the set of copper upon casting. Even the presence of a smallamount (of the order of a few per cent) of water vapor in the gasesadmitted to the melting chamber is objectionable, for at the temperatureprevailing in the chamber, water vapor decomposes into hydrogen andoxygen (particularly in the presence of carbon monoxide) and theresulting hydrogen may affect the set of the copper during casting.

The melting chamber atmosphere should be reasonably free of carbondioxide, since carbon dioxide reacts with molten copper to yield carbonmonoxide and cuprous oxide. A small amount of carbon dioxide in thepresence of a large amount of carbon monoxide may not be detrimental,since in the presence of the carbon monoxide the formation of cuprousoxide is for most practical purposes suiciently retarded.

The presence of decomposable hydrocarbons in the meltingchamberatmosphere is undesirable, since such hydrocarbons are cracked atthe prevailing temperature and carbon is deposited on the surface of themetal or on the under surface of the arch or on both. Such deposits ofcarbon, Whether'on the surface of the metal or on the undersurface ofthe arch, materially lower the melting rate of the furnace. Theilluminants present in coal gas or in enriched producer gas orwater gassuch as is available in most cities are examples of decomposablehydrocarbons which behave in this fashion.

It is also desirable to avoid the presence of sulphur in the meltingchamber atmosphere. Some sulphur (usually in the form of copper sulphateor sulphuric acid occluded in the cathode) is unmeager avoidablyintroduced into the melting chamber with the charge. The small amount ofsulphur so introduced is not objectionable, for it cooperates with theoxygen incorporated in the copper as it is withdrawn from the meltingchamber to produce the desired set of tough-pitch copper. The coppercharged to the melting chamber usually contains as much sulphur -as itis desirable to have, however, and so it is best to avoid the presenceof sulphur or sulphur compounds in the melting chamber atmosphere.

, The gas providing the non-oxidizing or reducing atmosphere in themelting chamber is admitted thereto through the inlet conduits 33, andpreferably is maintained in the melting chamber under a slight positivepressure of the order of IAO@ of an inch of water to prevent air orcombustion gases from leaking into the melting chamber.

Since the copper melted in the melting chamber is not 'allowed to comein contact with contaminants, it is substantially as pure as the metalcharged. The process is particularly adapted for melting electrolyticcopper cathodes, and when this material is used as the charge, themolten copper in the melting chamber is substantially oxygen-free. Thissubstantially oxygen-free copper is withdrawn through the furnace taphole 34 and the launder 35 to the casting equipment.

The copper owing through the launder is covered with a layer of charcoalto prevent it from becoming oxidized to an undesirable extent, but thecoverage of the copper by the charcoal is incomplete, so as to permitthe copper to be exposed to the air sufficiently to incorporate therein'a proper amount of oxygen to produce a flat-set upon casting andcooling. A number of variable factors, such as the temperature of themetal flowing through the launder, the rate of flow of metaltherethrough, and the presence of air currents in the Vicinity of thelaunder influence the amount of oxygen 'absorbed by the copper as itflows through the launder. variable factors, such as the amount ofsulphur present in the copper, affect the amount of oxygen required toproduce a fiat-set upon casting and cooling. Accordingly, it is notpossible to formulate precisely what proportion of the surface of thecopper flowing through the launder should be exposed to the air. Thiscan be determined, however, by the usual procedure of casting small testblocks and observing the set thereof upon solidifying. If the setindicates that too much oxygen is present in the copper, additionalcharcoal may be added to the launder, or if the set indicates adeficiency of oxygen, some of the charcoal may be raked from the surfaceof the copper in the launder. It has been found that in general about0.01% to 0.05%( oxygen by weight of the copper should be incorporated inthe copper to obtain the desired flat-set.

Although the test here employed is the same as that used in theheretofore common refining process, the amount of oxygen incorporated inthe molten copper is very much easier to control in the new process thanis the poling operation of the rening process.

The copper flowing from the launder 35 may be introduced into anysuitable casting equipment for casting into molds. Ordinarily a smallreservoir in the nature of a tilting furnace or ladle is interposedbetween the launder and the mold. Almost any of the pieces of equipmentOther Y acca-ce1 commonly in use forfthis purpose maybe employedr Forexample,l the copper fromV the launder-'mayibe introduced into a tiltingelectric furnace` from'` which it may be poured into the molds,oritlmayY be introduced into a pouring ladle suitably heated, forexample, byA anoil fiame; It has-been found that contact of the copperwith combustion gases in an oil' heated ladle is not objectionable,apparently-because `the copper remains in the ladle for so shortr aperiod of time that it does not become contaminated thereby.

AlthoughV the method of the invention-may be operatedlintermittently asa batch process, it is suited'- to continuous operation and is' mosteconomically practiced when carried out continuously. Thecopperoathodes` to be melted maybe charged continuously into the furnace, andimelted copper may be' continuously Withdrawnth'ereirom at substantiallythe same rate as the cathodes are charged.

The hooks of the initial starting sheets` of copper cathodes arepreferably out oif before charging the oathodes into the meltingchamber. Undesirable amounts of oxidizedcopper, copper sulphate, etc.,are frequently associated with these --hooks and'it'is'hence betternotto attempt to melt them in--practicing the present invention. Whateverslight amount of oxidized copper that be introduced into the bath ofmolten copper during charging and melting of' cathodes and the like isreadily reduced by the gaseous reducingatmosphere, so that the bath ofmolten.

copper in the meltingl chamber is for all practical' :ur-posessubstantially oxygen-free. In addition to copper cathodes, other formsof equally pure'substantially oxygen-free copper may'constituteallor-part of the copper charged into the melting chamber. Whereinsufficient sulphur is naturally present inthe copper to be melted, acontrolled amount oi sulphur may be incorporated iny the'molten copperin' the melting chamber; asV for example, by the controlled.introduction' of sulphur dioxide' gas or by the addition` of elementalsulphur along with the copper asA charged intoV the melting chamber.

Asideirom the usually minute amount of oxidized'copper present on thesurface of copper cathodes; the method of" the invention removesnoimpurities.fromv the copper. But the method or the` invention. doeseffectively reduce Whatever kamount of oxidized copper is ordinarilyassociatedwith the copper cathode. The surface of the' molten copper isexposed to the direct in.- iiuenceofthe gaseous reducing atmosphere andanyouprous oxide in the moltencopper is thereby reduced; Suchcuprousoxide tends naturally to migrate to the surface of the moltencopper, and this tendency is promoted by the agitation of the moltencopper asthe cathodes drop into it. When conducted as a continuousoperation, the method of the invention permits of marked fuel economy,higher output cf cast copper shapes and greatly increased furnace lifethan in the heretofore customary melting and refining proc- Theinvention eliminates the former operns of oxidizing and poling themolten copper their attendant diiculties, particularly in `,ontrollingthe quality oi the copper produced. The only variable control that needbe exercised in practicing the invention is the incorporation of oxygenin the molten copper withdrawn from the melting chamber, and thiscontrol is not diiiicult to maintain.

The method of the invention imposes no severe to nd treatmenton thefurnace refractories. The sub'- stantiall-y oxygen-free molten copperdoes lnot aifect they refractory lining of the meltingchamber, and noslagispresent to-attack'the-linirlg.V

Thefurnace is not repeatedly heated and cooled; as heretoforecustomaryfin meltingl copper cathodes, and-the furnace refractories areVhence not subject to thermal shock, and the extensive heat lossesinherent in the prior'art intermittentv operationare eliminated. Thelireof furnaces used in carrying out the invention is thereforemeas.-ured'inyears insteadof'months; as inthe case offurnacesused in theheretofore customary ree' ning process. Y Y

This application is a continuation-in-part of our. pending and allowedapplication Serial-No. 30`467 filed November 16, 1939.-

`We claim:

l. The method of producing substantiallyatset cast copper lshapes `whichcomprises introduce ing substantially oxygen-freel copper,y into the.

melting chamber of a fuel-fired mufllefurnace,r

heating and melting the copper therein largely., by means of radiantheat while maintainingl a.

non-oxidizing atmosphere vwithin thexmelting. chamber; withdrawingsubstantially oxygen-free moltenl copper from the meltingV chamber. and.

exposing itto an oxidizing atmosphere su.-

ciently to incorporate therein a proper amountY of oxygen` to produce aflat-set upon castingand.' cooling, and castingtlie resultingoxygen-bear ingmolten copper.` into a'suitable shape..

2. The method ofproducing substantially` flat set cast copper shapeswhichcomprises heating the melting chamber. of 'a fuel-redmuiefur.- naceto a temperature above the melting pointofcopper, maintaining a bathofsubstantially oxygen-freel molten copper in said melting cham-- ber,the surface ofv said bath of molten copperbeing free of slag,maintaining. intheA melting chamber above. the molten copper. therein. agaseous-'reducing atmosphere, introducing the sub--v stantiallyoxygen-free copper to be melted intoY the melting chamber under`conditions substan-A tially inhibiting the introduction of air intothe.chamber `and melting the copper so introduced-l while maintaining theYaforesaid slag-free bathofsubstaritially oxygen-free molten copper, withdrawing substantially oxygen-free molten copper from the meltingchamber. and exposing it to an oxidizing atmosphere suficiently toincorporate thereina proper amount of oxygen to produce a at-'setuponcastingand cooling, andcasting the resulting oxygen-bearing moltencopper vrinto a.

suitable shape..

3.'. The method of producing substantiallyhat?.r set cast copper shapeswhich comprises intro-V ducing copper cathodes into the melting chamberof a fuel-ii'red` muffle furnace, heating-rand melting the coppertherein largely by means ofheat radiated tothe exposed' surface of thecopper, maintaining the surface of the copper in the melting chambersubstantially free of reactive fused slag, maintaining a non-oxidizingatmosphere within the melting chamber, withdrawing y substantiallyoxygen-free molten copper from the melting chamber and exposing it to anoxidizing atmosphere sufficiently to incorporate therein a proper amountof oxygen to produce a flat-set upon casting and cooling, and castingthe resulting oxygen-bearing molten copper into a suitable shape,

4. The method of producing substantially flatset cast copper shapeswhich comprises introducing substantially oxygen-free copper into themelting chamber of a fuel-fired muiile furnace, heating and melting thecopper therein largely by means of heat radiated` to the exposed surfaceof the copper, maintaining a layer of finely divided refractory materialhaving a relatively high emissivity and good heat conductivity over thesurface of the molten copper in the melting chamber while at the sametime maintaining the surface of the molten copper free of any mediumimpeding the transfer of radiant heat thereto, maintaining anon-oxidizing atmosphere within the melting chamber, withdrawingsubstantially oxygen-free molten copper from the melting chamber andexposing it to an oxidizing atmosphere sufficiently to incorporatetherein a proper amount of oxygen to produce a fiat-set upon casting andcooling, and casting the resulting oxygen-bearing molten copper into asuitable shape.

5. The method of continuously producing substantially nat-set castcopper shapes which comprises continuously introducing substantiallyoxygen-free copper into the melting chamber of a fuel-red muiilefurnace, heating and melting the copper therein largely by means ofradiant heat while maintaining a non-oxidizing atmosphere within themelting chamber, continuously withdrawing substantially oxygen-freemolten copper from the melting chamber and exposing it to an oxidizingatmosphere suiciently to incorporate therein a proper amount of oxygento produce a flat-set upon casting and cooling, and continuously castingthe resulting oxygen-bearing molten copper into a suitable shape.

6. The method of producing substantially atset cast copper shapes whichcomprises introducng substantially oxygen-free copper into the meltingchamber of a fuel-lired muie furnace, heating Iand melting the coppertherein largely by means of radiant heat while maintaining anon-oxidizing atmosphere within the melting chamber, withdrawingsubstantially oxygen-free molten copper from the melting chamber throughan open launder, maintaining the surface of the copper in the launderpartially but incompletely covered with charcoal, controlling the areaof copper in the launder exposed to the air in a manner to permitincorporation in the copper of Va proper amount of oxygen to produce afiat-set upon casting and cooling, and casting the resultingoxygen-bearing molten copper into a suitable shape.

7. The method of producing substantially flatset cast copper shapeswhich comprises introducing substantially oxygen-free copper into amelting chamber of a furnace below a melting chamber arch, introducingand burning fuel in a combustion chamber above said arch in a manner toheat the arch and establish and maintain at its under surface atemperature of about 2500 F., whereby copper in the melting chamber ismelted largely by heat radiated thereto from the arch, withdrawingsubstantially oxygen-free molten copper from the melting chamber andexposing it to an oxidizing atmosphere sufficiently to incorporatetherein a proper amount of oxygen to produce a flat-set upon casting andcooling, and casting the resulting oxygen-bearing molten copper into asuitable shape.

8. The method of producing substantially flatset cast copper shapeswhich comprises introducing substantially oxygen-free copper into themelting chamber of a furnace below a melting chamber arch, maintaining anon-oxidizing atmosphere substantially free of hydrogen and decomposablehydrocarbons in the melting chamber, introducing and burning fuel in acombustion chamber above the arch in a manner to heat the arch andestablish and maintain at its under surface a temperature at least equalto the melting point of copper whereby copper in the melting chamber ismelted largely by heat radiated thereto from the arch, withdrawingsubstantially oxygen-free molten copper from the melting chamber andexposing it to an oxidizing atmosphere sufficiently to incorporatetherein a proper amount of oxygen to produce a Hat-set upon casting andcooling, and casting the resulting oxygen-bearing molten copper into asuitable shape.

9. The method of continuously producing sub. stantially flat-set castcopper shapes which comprises continuously introducing substantiallyoxygen-free copper into a melting chamber of a furnace below a meltingchamber arch, continuously introducing and burning fuel in a combustionchamber above said arch in a manner to heat the -arch and to establishand maintain at its under surface a temperature substantially `above themelting point of copper, whereby copper in the melting chamber is heatedand melted largely by heat radiated thereto from the arch, maintaining anon-oxidizing atmosphere substantially free of hydrogen and decomposablehydrocarbons and consisting predominantly of carbon monoxide andnitrogen in the melting chamber, maintaining the surface of the copperin the melting chamber substantially free of reactive fused slag,continuously withdrawing substantially oxygen-free molten copper fromthe furnace through an open launder, maintaining the surface of thecopper in the launder partially `but incompletely covered with charcoal,controlling the area of copper in the launder exposed to the air in amanner to lpermit incorporation in the copper of an amount of oxygenfrom 0.01% to 0.05% sufficient to produce a flatset upon casting andcooling, and casting the resulting oxygeinbearing molten copper into asuitable shape.

PHILIP M. HULME. ROBERT A. GHELARDI.

